What I say here may be considered a spoiler to some, so read at your own risk : this drama is an open-ended drama, meaning it's up to your interpretation as to what happens at the end of it.
It's a very short drama, but compact with tons of messed up emotions, romance, love triangles, and dilemmas that the characters experience throughout the whole show.

STORY: They did manage to squeeze the main characters stories into 9 short episodes, which is good, and was quite different from normal dramas which made it quite interesting. The sad part is that there wasn't enough room to discover any of the other characters stories (you could say Jin Joo, but that was only surface level plot that was revealed for her), which would have pulled a lot of people in.

ACTING: I liked Won Joon's crying scenes, you could feel the emotion coming off the screen. Great job. Other than that, the acting was fine, nothing much to discuss here.

Would I watch it again? — It does have rewatch potential, because many people analyze and read into the scenes, openings and create different unique stories as to what actually happened in the show. It's quite short, so you wouldn't be losing much time. To go back to the question, no, I personally would not watch it again for the sole reason that I do not like these types of endings and find them stupid. You can't decide whether to make it sad or not sad, so you leave it to the audience, not my cup of tea at all.

Would I recommend it? — If you are against open-ended dramas, don't watch it. You will be disappointed and sad that you didn't get to see a real ending. If you don't mind them or enjoy them even, I would definitely recommend it.